Future mobile systems are expected to support multiple radio access technologies, as well as diverse types of user equipments, including mobile phones, personal digital assistants (PDA), laptops, as well as wireless personal area networks, moving networks and vehicular networks.
Refer to FIG. 1 which illustrates a future scenario which illustrates a vehicular network 1, for example Ethernet onboard a bus, a non shown passenger has a personal local network (PAN) 2 to which a mobile phone and digital camera are connected. Another non shown passenger has also a PAN 3 to which an audio equipment and a video camera are connected. The PANs are wireless connected to an on-board wireless gateway WG that provides connectivity to an access router AR of a 4G wireless network or an access router of a wireless local area network (WLAN) 5, which in its turn provides connectivity to an access router of a land based IP backbone network 6. A 3G network 7 is also connected to the backbone network. A wireless lap top is connected to the 3G network. Vehicle movements entail hand-over for the vehicle WG, but may remain entirely hidden to passengers.
The term always best connected (ABC) in multi-access networks refers to the concept of defining a set of access selection criteria and mechanisms that allow users to get connected to various services in a nearly optimal manner irrespective of the terminal type [1]. For instance, in the vehicular network the on-board WG provides cellular connectivity through 2.5/3G cellular technologies to the 4G wireless network 4 on the country-side while it provides connectivity to the wireless local area network 5 at a central bus station. It is important to note that in such a situation, passengers may want to select access in order to being ‘best’ connected, even though they may use, for instance, an Ethernet interface from their respective user equipments to get connected to the WG.
Therefore, these types of vehicular or moving network scenarios can be thought of as ‘multi-hop’ scenarios in terms of the number of layer-2 (L2) connections between the end-user equipment and the access router (AR) of the IP-based backbone network. In such an environment it is a non-trivial issue how information about QoS can be provided to a QoS aware access selection algorithm which runs in an access selector of the user terminal.
Access selection has been the topic of intensive research recently; see for instance [2], where a multi-access architecture and associated decision algorithm based on QoS parameters (Quality of Service) are proposed. FIG. 2 shows the architecture proposed in [2]. A multimode terminal (MMT) 8 is capable of operating in three access networks; a satellite access network 9, a UMTS access network, and a GPRS access network. The MMT comprises terminal equipment (TE) 12, such as a laptop or any handheld terminal, a terminal interworking unit (T-IWU) 13, and three access specific mobile terminals 14-16. The T-IWU keeps track of the availability of access networks, is involved in all inter-access mobility procedures and cooperates with the access specific mechanisms for providing quality of service (QoS) over the multi-access network. Using certain parameters, including the condition of the radio coverage, and QoS perceived by the user, the MMT continuously executes procedures with the objective of selecting the most suitable access network. Any modification to said parameters leads to a change of access network. In order to ensure minimal modifications to the access systems most of the intelligence of the system is placed in the terminal.